Inductive coupling



june 259 946. CHRCHHAN I 294029599 INDUGTIVE COUPLING Filed 0G12. 2O 1942 Patented June Z5, 1946 INDUCTIV E COUPLING Benjamin Malcolm Charchian, New York, N. Y., assignor to Federal Telephone and Radio Corporation, Newark, N. J

Ware

., a corporation of Dela- Application October 20, 1942, Serial No. 462,720

(Cl. 175--359l 2 Claims. l

This invention relates to improvements in inductive ouplings, and more particularly to such couplings for use in connection with' medium high frequency circuits.

In the case of transformers or inductive couplings for use in circuits carrying relatively low frequency currents, the problem of unbalance due to the coupling is relatively unimportant as at such low frequencies the difference of a turn one way or another makes very little difference in the characteristic of the coupling and undesirable electrostatic coupling can be readily avoided by a suitable shield. In the case of the coupling of circuits carrying ultra-high frequencies, on the other hand, the question of the balance of the coupling is also relatively unimportant, as, in most cases, the coupling can readily be effected by means of a simple single link. In couplingcircuits carrying medium high frequency currents, however, transformers requiring several turns are needed but, in such circuits, the difierence of a half or quarter turn in a winding is still very important with respect to the question of balance and, moreover, the balance can also be upset by the electrostatic coupling between the coils and between the individual turns of each coil.

It is the primary object of the present invention to provide an inductive coupling, particularly for use at medi-um high frequencies, which will be perfectly balanced, and in which electrostatic coupling is substantially neutralized without the use of any shield.

The invention is described in more detail below, and as illustrated by way of example in the accompanying drawing in which:

Fig. 1 is a top plan View of a coupling formed in accordance with the present invention;

Fig. 2 is an end view of one of the coupling coils illustrated in Fig. 1;

Fig. 3 is a circuit diagram illustrating, by way of example, the manner in which my new' coupling may be used.

In Fig. 1 the coupling as a whole is generally indicated at I0, and will be seen to comprise two windings, one of which may be the primary I2 and the other the secondary I 4. The primary winding I2 as shown in Figs. l and 2 is formed of two identical cylindrical windings I5, IB, wound in opposite directions, connected at one end by a common lead I'I, and preferably positioned exactly parallel to one another. The secondary winding I4 isV formed identically with the primary winding I2 consisting of a pair of parallel cylindrical windings 2U, 22, interconnected at one end by a common lead 2I. The coils I8 and I8 are wound in opposite directions as indicated by the arrows A and B, and this opposite winding is also used in the construction of the secondary I4. The primary and secondary are juxtaposed so that, for example, the coils Iii and 22 are coaxial and the coils I6 and 2i] are also coaxial. The spacing between the primary and secondary will depend, of course, upon the type of coupling desired, and the number of turns in the primary and secondary windings can be chosen as desired. In any event, however, the number of turns in the coil I6 must be equal to the number of turns in th'e coil I8, and likewise the number of turns in the coils 20 and 22 must be the same. In order that all electrostatic coupling be completely neutralized, the parallel coils of each winding should be spaced together as closely as possible without touching.

The coupling described above can be used beftween balanced or unbalanced circuits and in all cases provides an arrangement in which perfectly balanced coupling is obtained and electrostatic-coupling is substantially neutralized. In using this coupling between an unbalanced circuit and a balanced circuit, it is unnecessary to provide a mid-point tap such as is now common.

An example of the use of my coupling in connecting an unbalanced circuit to a push-pull circuit is illustrated in Fig. 3 in which, moreover, the use of my coupling as a link coupling is also illustrated. In this figure the balanced couplings I il and I6 are used to interconnect a driver stage 24 to a push-pull amplifier 26. As a link coupling, two of my improved couplings are used and in this case the winding I 4 of the coupling I I) will be connected to the winding I4 of the coupling lil. The winding I 2 will lead to the grids of the arnplier stage 25 and the mid-tap 28 and the interconnecting lead 2 I will be connected to the pushpull cathodes. A completely balanced coupling is obtained by means of this arrangement, despite the fact that the driver stage 24 is unbalanced and the amplifier stage 26 is balanced. It will, of course, be understood that instead of the link coupling arrangement illustrated in Fig. 3, a suitable direct coupling using only one of my couplings is appropriate.

In certain instances, It may be advantageous to design the windings of my coupling to have a length substantially equal to one-quarter of the wavelength of the resonant frequency to which the circuit is tuned. In this case each winding consisting of two equal parallel coils may be considered as a resonant line folded back upon itself.

While I have illustrated a specic form of coupling and have shown a specic circuit embodying the same, it is to be understood that these illustrations have been given merely by way of example, and that the invention is not to be considered as limited thereto.

What I claim is:

1. A coupling comprising a primary winding consisting of a, pair of parallel single layer cylindrical coils of equal turns arranged side by side, wound in opposite directions and connected together at one end, and a secondary winding consisting of a pair of parallel single layer cylindrical BENJAMIN MALCOLM CHARCHIAN. 

